msm: kgsl: use seq_file for mem_entry debugfs

A process may have many kgsl mem entries in use. Outputing all of them
as a single debugfs seq_file record takes twice as long as necessary
because seq_file must retry higher order page allocations for the output
buffer until it is large enough to hold all mem entries.

Additionally, process_mem_print() currently holds the spinlock
private->mem_lock during this process. This is too much time to
disable interrupts, and prevents locking mutex in print_mem_entry.

Change the kgsl_mem_entry debugfs functions to output one entry at a
time. Then the seq_file only need to kmalloc one page regardless of
the number of kgsl_mem_entries.

CRs-Fixed: 1073673
Change-Id: I2907495b65e62d95a892741aed008048bb86aced
Signed-off-by: Santhosh Punugu <spunug@codeaurora.org>